Getting started with Python and QGIS 3 can be a bit overwhelming. In this post we give you a quick start to get you up and running and maybe make your PyQGIS life a little easier.

There are likely many ways to setup a working PyQGIS development environment---this one works pretty well.

Contents

Requirements

  • OSGeo4W Advanced Install of QGIS
  • pip (for installing/managing Python packages)
  • pb_tool (cross-platform tool for compiling/deploying/distributing QGIS plugin)
  • A customized startup script to set the environment (pyqgis.cmd)
  • IDE (optional)
  • Emacs (just kidding)
  • Vim (just kidding)

We'll start with the installs.

Installing

Almost everything we need can be installed using the OSGeo4W installer available on the QGIS website.

OSGeo4W

From the QGIS website, download the appropriate network installer (32 or 64 bit) for QGIS 3.

  • Run the installer and choose the Advanced Install option
  • Install from Internet
  • Choose a directory for the install---I prefer a path without spaces such as C:\OSGeo4W
  • Accept default for local package directory and Start menu name
  • Tweak network connection option if needed on the Select Your Internet Connection screen
  • Accept default download site location
  • From the Select packages screen, select: Desktop -> qgis: QGIS Desktop

When you click Next a bunch of additional packages will be suggested---just accept them and continue the install.

Once complete you will have a functioning QGIS install along with the other parts we need. If you want to work with the nightly build of QGIS, choose Desktop -> qgis-dev instead.

If you installed QGIS using the standalone installer, the easiest option is to remove it and install from OSGeo4W. You can run both the standalone and OSGeo4W versions on the same machine, but you need to be extra careful not to mix up the environment.

Setting the Environment

To continue with the setup, we need to set the environment by creating a .cmd script. The following is adapted from several sources, and trimmed down to the minimum. Copy and paste it into a file named pyqgis.cmd and save it to a convenient location (like your HOME directory).

@echo off
SET OSGEO4W_ROOT=C:\OSGeo4W3
call "%OSGEO4W_ROOT%"\bin\o4w_env.bat
call "%OSGEO4W_ROOT%"\apps\grass\grass-7.4.0\etc\env.bat
@echo off
path %PATH%;%OSGEO4W_ROOT%\apps\qgis-dev\bin
path %PATH%;%OSGEO4W_ROOT%\apps\grass\grass-7.4.0\lib
path %PATH%;C:\OSGeo4W3\apps\Qt5\bin
path %PATH%;C:\OSGeo4W3\apps\Python36\Scripts

set PYTHONPATH=%PYTHONPATH%;%OSGEO4W_ROOT%\apps\qgis-dev\python
set PYTHONHOME=%OSGEO4W_ROOT%\apps\Python36

set PATH=C:\Program Files\Git\bin;%PATH%

cmd.exe

You should customize the set PATH statement to add any paths you want available when working from the command line. I added paths to my git install.

The last line starts a cmd shell with the settings specified above it. We'll see an example of starting an IDE in a bit.

You can test to make sure all is well by double-clicking on our pyqgis.cmd script, then starting Python and attempting to import one of the QGIS modules:

C:\Users\gsherman>python3
Python 3.6.0 (v3.6.0:41df79263a11, Dec 23 2016, 07:18:10) [MSC v.1900 32 bit (In tel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import qgis.core
>>> import PyQt5.QtCore

If you don't get any complaints on import, things are looking good.

Installing pb_tool

Open your customized shell (double-click on pyqgis.cmd to start it) to install pb_tool:

python3 -m pip install pb_tool

Check to see if pb_tool is installed correctly:

C:\Users\gsherman>pb_tool
Usage: pb_tool [OPTIONS] COMMAND [ARGS]...

  Simple Python tool to compile and deploy a QGIS plugin. For help on a
  command use --help after the command: pb_tool deploy --help.

  pb_tool requires a configuration file (default: pb_tool.cfg) that declares
  the files and resources used in your plugin. Plugin Builder 2.6.0 creates
  a config file when you generate a new plugin template.

  See http://g-sherman.github.io/plugin_build_tool for for an example config
  file. You can also use the create command to generate a best-guess config
  file for an existing project, then tweak as needed.

  Bugs and enhancement requests, see:
  https://github.com/g-sherman/plugin_build_tool

Options:
  --help  Show this message and exit.

Commands:
  clean       Remove compiled resource and ui files
  clean_docs  Remove the built HTML help files from the...
  compile     Compile the resource and ui files
  config      Create a config file based on source files in...
  create      Create a new plugin in the current directory...
  dclean      Remove the deployed plugin from the...
  deploy      Deploy the plugin to QGIS plugin directory...
  doc         Build HTML version of the help files using...
  help        Open the pb_tools web page in your default...
  list        List the contents of the configuration file
  translate   Build translations using lrelease.
  update      Check for update to pb_tool
  validate    Check the pb_tool.cfg file for mandatory...
  version     Return the version of pb_tool and exit
  zip         Package the plugin into a zip file suitable...

If you get an error, make sure C:\OSGeo4W3\apps\Python36\Scripts is in your PATH.

More information on using pb_tool is available on the project website.

Working on the Command Line

Just double-click on your pyqgis.cmd script from the Explorer or a desktop shortcut to start a cmd shell. From here you can use Python interactively and also use pb_tool to compile and deploy your plugin for testing.

IDE Example

By adding one line to our pyqgis.cmd script, we can start our IDE with the proper settings to recognize the QGIS libraries:

start "PyCharm aware of Quantum GIS" /B "C:\Program Files (x86)\JetBrains\PyCharm 3.4.1\bin\pycharm.exe" %*

We added the start statement with the path to the IDE (in this case PyCharm). If you save this to something like pycharm.cmd, you can double-click on it to start PyCharm. The same method works for other IDEs, such as PyDev.

Within your IDE settings, point it to use the Python interpreter included with OSGeo4W---typically at: %OSGEO4W_ROOT%\bin\python3.exe. This will make it pick up all the QGIS goodies needed for development, completion, and debugging. In my case OSGEO4W_ROOT is C:\OSGeo4W3, so in the IDE, the path to the correct Python interpreter would be: C:\OSGeo4W3\bin\python3.exe.

Make sure you adjust the paths in your .cmd scripts to match your system and software locations.

Workflow

Here is an example of a workflow you can use once you're setup for development.

Creating a New Plugin

  1. Use the Plugin Builder plugin to create a starting point [1]
  2. Start your pyqgis.cmd shell
  3. Use pb_tool to compile and deploy the plugin (pb_tool deploy will do it all in one pass)
  4. Activate it in QGIS and test it out
  5. Add code, deploy, test, repeat

Working with Existing Plugin Code

The steps are basically the same was creating a new plugin, except we start by using pb_tool to create a new config file:

  1. Start your pyqgis.cmd shell
  2. Change to the directory containing your plugin code
  3. Use pb_tool create to create a config file
  4. Edit pb_tool.cfg to adjust/add things create may have missed
  5. Start at step 3 in Creating a New Plugin and press on

Troubleshooting

Assuming you have things properly installed, trouble usually stems from an incorrect environment.

  • Make sure QGIS runs and the Python console is available and working
  • Check all the paths in your pygis.cmd or your custom IDE cmd script
  • Make sure your IDE is using the Python interpreter that comes with OSGeo4W

[1] Plugin Builder 3.x generates a pb_tool config file

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